This application is related to Japanese Patent Application No. 11-184466, filed Jun. 29, 1999.
1. Field of the Invention
The present invention generally relates to internal combustion engines for land vehicles and, more particularly, to internal combustion engines for powering snowmobiles.
2. Description of Related Art
Snowmobiles are popular land vehicles that are operated primarily in the winter over snowy terrain. A typical snowmobile comprises a frame assembly, a drive assembly that is coupled to the frame assembly and engages a ground surface to propel the snowmobile, an internal combustion engine supported by the frame for powering the snowmobile, and a transmission for transmitting power from the engine to the drive assembly.
In the past, two-stroke engines were typically used to power snowmobiles. More recently, however, four-cycle engines have been used, primarily for their reduced emissions. The four-stroke snowmobile engine typically comprises a crankcase assembly, a crankshaft supported for rotation within the crankcase assembly, a cylinder block assembly that extends from the crankcase, and a cylinder head assembly connected to an end of the cylinder block opposite the crankcase. A camshaft is typically supported for rotation within the cylinder head to actuate a valve mechanism of the engine.
The crankshaft typically includes a drive sprocket located at one end of the crankshaft. The camshaft may include a driven sprocket. The camshaft is driven from the crankshaft by a timing chain or belt that extends around the drive sprocket and the driven sprockets.
The transmission of the snowmobile is typically driven from the end of the crankshaft at which the drive sprocket is located. This end of the crankshaft typically has a relatively large diameter to transmit torque from the engine to the transmission. Because the drive sprocket is located at this same end of the crankshaft, the diameter of the drive sprocket is also typically relatively large.
For proper actuation of the valve mechanism, the driven sprockets of the camshafts generally must have a diameter that is twice the diameter of the drive sprocket. As a result, the size of the cylinder head which typically contains camshaft and driven sprockets must be relatively large. This undesirably increases the overall size of the engine.
In addition, in order to minimize engine vibrations during operation of the snowmobile, it is preferable that the center of gravity of the engine be located in the proximity of the cylinders (e.g., at the central axis of the cylinder in a single cylinder engine, or at the center of the group of cylinders in a multi-cylinder engine). However, because the large-diameter end of the crankshaft extends from one side of the engine to power the transmission and the camshafts, the center of gravity of the engine typically is offset towards the end of the crankshaft.
A need therefore exists for a snowmobile having an improved four-cycle engine.
In accordance with one aspect of the present invention, a snowmobile is provided comprising a frame assembly and a drive assembly coupled to the frame assembly. The drive assembly includes a drive belt adapted to contact a ground surface to propel the snowmobile over the ground surface. An internal combustion engine is supported by the frame assembly. The engine comprises a crankcase, a crankshaft rotatably journaled within the crankcase, a cylinder block assembly extending from the crankcase, and a cylinder head assembly connected to an end of the cylinder block opposite the crankcase. A cam drive mechanism including at least one camshaft is rotatably journaled within the cylinder head assembly. A transmission is coupled to the crankshaft to transmit power from the engine to the drive assembly. The cam drive mechanism is connected to the crankshaft at a first end portion of the crankshaft. The transmission is connected to the crankshaft at a second end portion of the crankshaft opposite the first end portion.
In accordance with another aspect of the present invention, a snowmobile is provided comprising a frame assembly and a drive assembly coupled to the frame assembly. The drive assembly includes a drive belt adapted to contact a ground surface to propel the snowmobile over the ground surface. An internal combustion engine is supported by the frame assembly. The engine comprises a crankcase, a crankshaft rotatably journaled within the crankcase, and a cylinder block assembly extending from the crankcase and defining a cylinder bore. A piston is positioned for reciprocating movement in the cylinder bore. A connecting rod is coupled to the piston and the crankshaft to transmit motion therebetween. A cylinder head assembly is connected to an end of the cylinder block opposite the crankcase, and a cam drive mechanism including at least one camshaft is rotatably journaled within the cylinder head assembly. A transmission is coupled to the crankshaft to transmit power from the engine to the drive assembly. The transmission and the cam drive mechanism are coupled to the crankshaft on opposite sides of the connecting rod.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiment which follows.